Bulls and Cows, known also as Cows and Bulls or Pigs and Bulls
is an old code-breaking paper and pencil game for two players, similar to Mastermind.

It is a game with numbers that may date back a century or more. It is played by
two opponents. The game can also be played with 3 digits instead of 4.

On a sheet of paper, the players each write a 4-digit secret number. The digits
must be all different. Then, in turn, the players try to guess their opponent's
number who gives the number of matches. If the matching digits are on their right
positions, they are "bulls", if on different positions, they are "cows". Example:

Secret number: 4271

Opponent's try: 1234

Answer: 1 bull and 2 cows. (The bull is "2", the cows are "4" and "1".)

The first one to reveal the other's secret number wins the game. If the "first"
player finds the number, the "second" has one more move to make and if he also succeeds,
the result is even.

The secret numbers for Bulls and cows are usually 4-digit-numbers, but the game
can be played with 3 to 6 digit numbers (with 5 and 6 digit numbers it is more difficult than
with 4).

The game may also be played by two teams of 2-3 players. The players of every team
discuss before making their move, much like in chess.

Because the game has simple rules, while it is difficult and entertaining, there
are many computer variants; it is often included in telephones and PDAs.

Why did I make a new computer variant?

I got the text above from Wikipedia. Yes it's true that there are many computer variants, but in all of them there is only one player who tries to guess the number generated by the computer. In my online variant there are two players, you and the computer. You will try to guess the computer's secret number and the computer will try to guess your secret number. Enjoy!

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